This invention relates to a process for preparing electrophotographic imaging members. More specifically the invention is directed to an electrophotochemical method for preparing electrophotographic imaging members comprising a layer of selenium having a periodic spatially modulated thickness.
The formation and development of images on an imaging member of photoconductive materials by electrostatic means is well known. The best known of the commercial processes, more commonly known as xerography, involves forming an electrostatic latent image on the imaging layer of an imaging member by first uniformly electrostatically charging the surface of the imaging layer in the dark and then exposing this electrostatically charged surface to a light and shadow image. The light struck areas of the imaging layer are thus rendered relatively conductive and the electrostatic charge selectively dissipated in these irradiated areas. After the photoconductor is exposed, the latent electrostatic image on this image bearing surface is rendered visible by development with a finely divided colored electroscopic powder material, known in the art as "toner". This toner will be principally attracted to those areas on the image bearing surface having a relative polarity opposite to the charge on the toner and thus form a visible powder image. The developed image can then be read or permanently affixed to the photoconductor in the event that the imaging layer is not to be reused. This latter practice is usually followed with respect to the binder-type photoconductive films where the photoconductive insulating layer is also an integral part of the finished copy.
In so-called "plain paper" copying systems, the latent image can be developed on the imaging surface of a reusable photoconductor or transferred to another surface, such as a sheet of paper, and thereafter developed. When the latent image is developed on the imaging surface of a reusable photoconductor, the developed image is subsequently transferred to another substrate and then permanently affixed thereto. Any one of a variety of well-known techniques can be used to permanently affix the toner image to the transfer sheet, including overcoating with transparent films and solvent or thermal fusion of the toner particles to the supportive substrate.
In the most popular of the xerographic systems of the type referred to above, the imaging member comprises a photoconductive insulating layer of amorphous selenium on a suitable conductive substrate. Such photoconductive insulating layers are generally prepared by vacuum deposition of selenium under carefully controlled conditions. These vacuum deposition techniques generally do not readily lend themselves to the continuous manufacture of photoconductive image members. Even under carefully controlled conditions, vacuum deposition of photoconductive insulating layers of amorphous selenium may encounter difficulties. For example, lack of uniformity in deposition can lead to so-called "pin holes" in the selenium layer. Spattering of molten selenium from the crucible in the deposition chamber can cause an uneven deposition and blemishes in the surface of the imaging layer. Nor is it uncommon for the vacuum deposition chamber to be contaminated with dust particles which codeposit along with the selenium on the receptive substrate, thus, forming additional imperfections in the surface of the imaging layer. Where such deposition does proceed as intended, the selenium forms a uniform continuous deposit on the conductive substrate.
Amorphous selenium deposits may also be reportedly prepared by electrochemical deposition techniques. Unfortunately deposits prepared in this manner have generally not been suitable for use in electrophotography either because of a high dark decay rate (see A. K. Graham et al, J. Electrochem. Soc., 106:8, 651, 1959) or the lack of uniformity in the coating (see U.S. Pat. No. 2,649,409).
There are also known in the art electrophotographic imaging members wherein the photoconductive insulating layer has a periodically varying thickness. The present application is directed to a process for forming such a member by electrophotochemical means.